Stereotype mat



Sept. 26, 1961 P. B. HANSEN ETAL 3,001,899

STEREOTYPE MAT Filed April 16, 1956 2 Sheets-Sheet 1 deal 2x15066330@139 W Qfibgya Sept. 26, 1961 P. s. HANSEN ETAL 3,001,399

STEREOTYPE MAT Filed April 16. 1956 2 Sheets-Sheet 2 United StatesPatent 3,001,899 STEREOTYPE MAT Paul B. Hansen, Neenah, and Sedgwick C.Rogers, Appleton, Wis., assign'ors to Kimberly-Clark Corporation,Neenah, Wis., a corporation of Wisconsin Filed Apr. 16, 1956, Ser. No.578,293 5 Claims. (Cl. 154-46) The present invention relates generallyto stereotype mats and is particularly, concerned with an improvedcomposite stereotype 'mat and backing and with methods for manufacturingthe improved backing.

In the usual process for making a stereotype plate for newspaperprinting or the like, there is first made a stereotype matrix or matfrom which the metal plates are cast. This stereotype mat, or flong asit is some-' times called, is usually made of a moisture-permeablepaperboard material of suitable thickness to provide Following thepressing operation, the mat is dried and formed, usually by a processwhich includes placing the imprinted mat in a curved former and dryer,sometimes termed the scorcher. Generally, the dryer includes a curved,foraminous surface which is connected to a source 7 of reduced pressurein order that the moisture liberated during the heating operation willbe drawn oifthrough the back of the mat.

Furthermore, it is the current practicein various printing industriestoshrink stereotype mats quite substantial-- ly in order to reduce thesize of the printed image and the amount of paper required intheprinting operation. When this practice is followed, it is usuallydesirable to dry the mat in two steps, initially heating the. flat matto drive off some of the moisture and then placing'the mat in the curveddryer mentioned above to complete the drying and forming of the mat.Since the actual stereotype plate is made by casting molten type metalagainst the curved paperboard mat as a matrix, it is necessary that themat be completely dried prior to the casting operation and that it besufiiciently hard and rigid to resist the casting pressure.

Since the forming and casting operations involve quite substantialpressures, it has been found necessary to provide some meansforpreventing buckling or yielding of the mat in the nonprinting areas, andparticularly those areas which are of substantial dimensions. the mostcommon means for packing or backing the mat consists in attaching thinstrips of paper felt, along the rear surface, in those areas of the matwhich have rather large nonprinting areas. This packing is usuallyv doneafter the mat has been molded and, if a pre-drying step is used, betweenthe first drying and the final drying against the curved former.Reinforcement of nonprinting areas too small to bepacked with feltstrips is sometimes accomplished by running the point of a pencil on theback side of the mat in those areas to form nonplanar areas in the faceof the mat which will resist buckling more effectively.

The hand packing of stereotype mats mentioned above is inherently timeconsuming and costly and, of even greater importance, it must be done ata time when every minute is vital, particularly in connection with Inpractice, r

Patented Sept. 26, 1961 newspaper printing. Further, the packing of amat in this manner requires the services of skilled workmen who must useconsiderable judgment in selecting the areas to be packed and inapplying the packing material properly.

A recent development in the solution of the problem of hand packingstereotype rnats has involved the use of a multi-ply, resin impregnatedpaper backing for the mat which is formed integrally with the mat andwhich eliminates the need for hand packing. The present inventionrelates to an improvement in the subject matter thereof.

It is the primary object of the present invention to provide an improvedtype of backing for a stereotype mat, which is completely moldable withthe stereotype mat during the forming operation, and which can be setduring the drying operation to provide a unitary structure with thestereotype mat having adequate strength and rigidity to resist the,pressures produced during casting operation, and which is adapted. to beheld securely against the mat throughout the making of the composite matand the subsequent uses thereof.

FIGURE 1 is a view in perspective of a portion of a lockup, illustratingone manner in which the mat, backing and molding composition arearranged in the practice of the invention.

FIGURE 2 is a view in perspective of a composite mat in accordance withthe invention, with the backing attached.

FIGURE 3 is a fragmentary view in elevation of the assembly duringpressing or molding of the mat about the printing form. e

FIGURE 4 is an enlarged cross-sectional view of a portion of the backedmat after its removal from the molding press.

FIGURE 5 is a fragmentary view of the backed mat during its formation inthe dryer.

FIGURE 6 is an end view of a dried and formed mat embodying thisinvention.

In the present invention, a paperboard mat or fiong of the type nowcommonly used is provided with a paper backing preferably consisting ofa plurality of plies of creped, cellulosic tissues having dispersedtherein a resinand of taking a permanent set in the printing'areas ofthe mat to provide the necessary rigidity and space depthcharacteristics in such areas, but still the backing'retains itsresiliency so as to provide the desired bulk in the portions overlyingthe nonprinting areas of the mat. Furthermore, when applied to ashrink-type flong, the

shrinkage of the flong and backing which takes place during drying isvery nearly the same as the unpacked mat or fiong alone. It should beunderstood, however,

that the invention is also adapted for use with stereo-type mats thatare not shrunk during their processing.

The preferred material for the backing consists of a plurality of pliesof thin, creped cellulosic tissue having an air dry basis weight, beforecreping, within the range of from about 5 to 10 pounds per standardreamof 480 sheets, each 24 by 36 inches, having a crepe ratio gen- 7 erallyin the range from 1.3 to 2.5, and containing a resinous substance of thetype and amount disclosed hereinafter.

The proper selection of a resinous substance to be used in the backingis critical to the proper performance -of the backing when applied to astereotype mat or fiong.

First of all, it is essential that the several plies of,

the backing be adequately bonded together during the drying of. thernulti-ply sheet after it is impregnated with the resinous substance,and preferably that sufficient tack remain in the backingto provide aneffective bonding of thebacking to the fiong when the two are pressedtogether during the initial pressing or rolling of the two in thelockup, which is generally a cold molding operation. In, this respect,it is intended herein that tack be defined as including the capabilityof becoming adhesive in the presence of moisture and the term is.

not confined to the description of an actual state of adhesiveness.

It is also necessary that the backing have adequate flexibility andmoldability to satisfactorily perform its intended purpose and yet havesufficient stiffness, as supplied to the user, to facilitate handling inapplying the backing to the flong. Then too, the binder used in.the.backing must be water soluble or dispersible in order to respond to thewater in the sheet during initial formation of the multi-ply sheet toprovide the proper bonding action between the several plies and, also,to respond to the moisture in the stereotype mat during the cold moldingoperation in the lockup to permit passage of the water from thestereotype mat through the backing material and to bond the two togetherduring molding operation in the lockup. Consequently, it is essentialthat the resin treated backing be highly water sensitive and that itrapidly develop a high degree of adhesiveness or tackiness with arelatively small amount of moisture.

It is also very important that the thermosetting resinin the bindermaterial for the backing be susceptible to relatively small-advancementduring the necessary drying step in initially forming the multi-plybacking, as, well as during the ordinary shelf life of the finishedbacking which may be expected to be as much as six months or evenlonger. This necessary characteristic of the thermosetting resin isparticularly important in providing for a wide range of advancement orcure during the actual use of the backing with a stereotype flong,especially in connection with the final scorching of the composite fiongand backing. In this respect, however, it should be under stood that thethermosetting resin should not be too green initially, that is, itshould not be in too low a state of polymerization because it will thensaturate the fibers of the tissue and produce a very soft and limpproduct, which will have insuflicient bonding between the plies.

Furthermore, it is essential that the backing retain its molded shapeafter it is removed from the lockup, in order that it maintain thespace-depth characteristics acquired during the cold molding operationthroughout the final drying and curing of the composite mat and backingand thereby provide better plate reproduction.

Finally, the resinous binder for the backing material.

should be essentially thermosetting or irreversible in nature attemperatures within a range of practical operation for the final dryingor scorching step, which temperatures are governed, at least in part, bya consideration of possible damage by heat to the fibers in the flong.

and backing.

It is seen from the foregoing that the requirements for the binder usedin the backing sheet are quite critical and, consequently, it has beenan extremely difiicult task to provide a binder material which willsatisfy all of the requirements and still be usable commercially. One

of the more important advantages of the present invention is theprovision of a binder material which reduces the criticality of thecharacteristics of the binder constituents and thereby greatly improvesits commercial value, particularly with respect to a very substantialextension of the useful life of the backing.

The present invention provides an impregnating material for a sheet oflow density, compressible material which meets all of the abovedescribed requirements and which combines with the sheet to provide astereotype mat backing of improved characteristics. Generally, thisinvention provides for the addition to a sheet of the type described,preferably a plurality of plies oftissue, of a resinous materialcomprising a blend of: a thermally 35 percent, such percentages beingbased on the dry solids weight. The resinous impregnate is added to.thesheet inan amount of from about 15 to 75 percent, based on the dryweight of the combined materials in the impregnateand in the tissuesheet. It should be noted that the use of the hydrophilic polymeric orcopolymeric additive in an amount much greater than the 35 percentstated above makes the impregnate too viscous to properly, saturate thesheet in a satisfactory manner and, also, makes the impregnated sheetmore sensitive to moisture than is desired in a satisfactory backing fora stereotype mat. The amount of hydrophilic additive use ,v within thestatedrange, will depend somewhat on the amount of solids in theimpregnating material or saturant. A reduction of the solids content inthe saturant will, of,

course, allow the use of a greater percentage of hydrophilic additivewithout making the impregnate too viscous or moisture sensitive. Theusable amount ofhydrophilic material will also be controlled to someextent by the method available for drying the impregnated sheet.

The irreversible resin in the impregnate, such as phenol-aldehyde orblends thereof, constitutes the major portion of the blend and isprimarily intended to provide the necessary strength for the backing toresist the casting pressures incurred during the forming of a metal typeplate from the stereotype matrix, although such resin also affords acertain amount of adhesion between the plies and between the backing andthe mat. In order to provide the best space depth characteristics forthe stereotype mat through utilization of a maximum degree of cure ofthe thermosetting resin in the scorcher, itis essentialthat the resin beinitially provided in the finished backing with a suitable degree ofcure, i.e. inan amount just sufiicient to afford the proper rigidity tothe backing sheet for handlingand for withstanding the pressures of thecold molding of the stereotype mat and backing a unit, And, aspreviously indicated, to provide a commercially acceptable backinghaving such characteristics.

it isnecessary that the thermosetting resin be prevented from becomingtoo far advanced in'its degree, of cure prior to its ultimate use by thestereotyper, which maybe six months or even a year.

It has been found that the use of a thermosetting resin alone, such as aphenol-aldehyde, is not entirely satis-.

factory, particularly in that if the original backing is made plies tostay together and to the resulting inadequatebondbetween the backing and.the mat; As a result, therange of ;usefulness of a .thermosettingresin.suchias; aphenol- L aldehyde; isrquite restricted and: the. state. ofrthei resin at the. time ofimpregnatingi the. backing sheet is-iquitecritis 1.

cal. It is not only diiiicult to properly control the characteristics ofthe resin at the time of impregnation, but it is also a considerableproblem to preserve the impregnated sheet in a useable state wherein thesheet is malleable, that is, capable of bearing a load and retaining theform assumed under such load after it is removed. A sheet impregnatedsolely with a thermosetting resin is capable of retaining this requiredcharacteristic for a very limited time even under the most favorableconditions.

The difficulties mentioned above have been overcome by introducing othermaterial into the resinous impregnate for the backing which, in effect,enhances the shelf life of the backing and greatly improves the bondingof' the plies together as well as to the stereotype mat. It has beenfound that by adding to the thermosetting resin a hydrophilic polymer orcopolymer, such as an alkali salt of a styrene-maleic anhydridecopolymer, there is thereby achieved a very desirable control of thecharacteristics of the backing. The added substance not only prolongsthe water sensitivity of the impregnated sheet, thereby prolonging itsshelf life, but also broaden the range of usefulness of the impregnatein that it makes it effective at lower moisture contents withoutsacrificing the required strengthening or stiffening of the sheet. Thehydrophilic additive also contributes to the ultimate strength of thecomposite mat and backing. One of the more important effects notedthrough the addition of a hydrophilic polymer or copolymer to thethermosetting resin is the reduction in the criticality of the'rate ofadvancement of the thermosetting resin. The effectiveness of theimpregnated sheet as a satisfactory backing for a stereotype mat is nolonger so seriously afiected by the advancement of the thermosettingresin either in the impregnating bath or that occurring'during theperiod between the formation of the sheet and its use as a backing and,consequently, a much broader selection is oifered in the character ofthe resin used and a much longer period of usefulness is realized forthe finished backing. The use of a hydrophilic polymeric or copolymericadditive in the impregnate also affords the use of broader ranges inconnection with the thermosetting resin content, the amount of moistureextraction, and the pH of the impregnate, while providing a satisfactorybacking for a stereotype mat. Further, the hydrophilic additive servesas a very effective binder for the several plies of the backing and forbonding the backing to the stereotype mat,

The thcrmosetting resins which have been found suitable for use in theimpregnate are the alkaline catalyzed one-step phenol-aldehyde type. Therate of the reaction or cure of these resins can be reduced by adjustingthe pH downward to neutrality or slightly above. In this respect, with apH of from 7.0 to about 7.3 there is a noticeable beneficial effect onthe shelf life of the backing sheet, i.e. retention of tack andretardation of advancement of the resin.

Then too, it has been found that the addition of a partially hydrolyzedpolyvinyl alcohol to the blend of phenol-aldehyde and hydrophilicpolymeric or copolymeric additive, in relatively small amounts, isadvantageous in many instances in that it aids in the uniformdistribution of the resinous material throughout the backing sheet. Theaddition of the polyvinyl alcohol is primarily an expedient arising outof the particular process used in impregnating the backing sheet.Consequently, the polyvinyl alcohol can be readily eliminated where theuniform distribution of the impregnate throughout the sheet is not aproblem.

The irreversible resin used is in a low state of polymerization, and issubject to a very slow rate of advancement at temperatures below about20 C. In terms of the standard dilutability test for measuring molecularweight with respect to water-soluble resins, the irreversible resin usedhas a dilutability within the range of from I about 2 to 1 to about 6 to1 The steretoype mat backing may be made of one or more sheets ofsuitable material, but preferably is in the form of a multi-ply tissuesheet comprising from about 3 to 20 plies of creped cellulosic tissuehaving an air dry change the structural characteristics of the multi-plysheet' or its individual plies. The impregnated sheet is then dried bysuitable means.

In a preferred form of the invention whioh has been successfully tested,a stereotype mat backing of the type described was made from 9 plies ofcreped cellulosic tissues made from chemical pulp, each individual sheethaving an uncreped, drier basis weight of 5.9 pounds per standard reamof 480 sheets, 24 x 36 inches, and a crepe ratio beforeimpregnation ofapproximately 2.3. Thus the basis weight of the creped material wasapproximately 13.5 pounds per standard ream.

The superposed sheets were impregnated by passage through a bathcontaining a resinousbonding agent comprising percent of a one-stepphenol-aldehyde resin, 7

percent of a sodium salt of styrene-maleic anhydride copolymer, such as*Scriptite 50 sold by Monsanto Chemical Co., and 3 percent of a watersoluble polyvinyl alcohol, such as Elvanol 51-05 sold by E. I. du Pontde Nemours & Co., the percentages expressed on the basis of dry solidscontent. The polyvinyl alcohol was added to prevent migration of theresinous impregnate during the drying of the backing sheet and therebyprovide uniformv distribution of the resin in the sheet. However, thisproblem arose primarily because of the particular drying method Iemployed, and themed for a control element such as polyvinyl alcohol maybe eliminated by using a difierent improvement is noted with respect tothe ability of the thermosetting resin to retain its low state ofpolymerization over a longer period, between the formation of the 1backing and its use, and thereby affords longer storage of the backingwithout advancement of the resin.

Excess liquid was removed from the backing by passing it between squeezerolls, to provide a total resin content of approximately 42 percent ofthe weight of the finished backing sheet on a volatile-free basis. Theimpregnated sheet was then dried by circulating hot air around the sheetat 300 F. for about 5 minutes.

The resin treated creped Wadding sheets were used as a backing inconnection with stereotype mats for a rotary press for printingnewspapers. Generally, the advantages of the backing are realized byplacing the backing on the side of the stereotype mat opposite thatfacing the type in the lockup and pressing the backing and mat againstthe type face in a cold molding operations The backing thereby becomessecurely bonded to the back of the mat.

A more detailed explanation of the use of the backing in connection withrotary press plate formation will be had with respect to the apparatusshown in the accompanying drawings. in the lockup or printing form 10 aheavy metal chase 11 for holding the printing elements in place.Substantially flush with the level of the case 11 is an arrangement ofAs seen in FIG.. 1, there is included Y printing elementsincluding-typeslugs 12, each of which contains raised type faces 13and'engraving 14 separated from the type 12 by means of a spacer 16, anda second set of type 17 with its raised typefaces 18.

A stereotype mat 19 in the form of a permeable paperboard mat ordinarilycontaining from about to 40 percent by weight of free moisture andhaving a thickness of from. about .024 to .040 inch, is placed over theprinting form 10; The resin-impregnated backing 21 is then placedagainst the back of, the mat 19 and a-compressible cushion ormoldingcombination 22, which may comprise one or more sheets ofyieldablematerial such as cork, or a mixture of cork and syntheticrubber and/ or fabric, is placed over the backing sheet 21. Ifdesired anunimpregnated ply of tissue or the, like may be used on one or bothsurfaces of the backing 21 to facilitate handling of the backing.

Mats of the type now generally used for newspaperwork shrinkconsiderably upon drying for the reasons given above, depending in partupon their relative moisture content. This shrinkage occurs to thegreatest degree transversely of the mat, i.e. at right angles to themachine direction of the fibers. The shrinkage in the lengthwisedirection is ordinarily about half of what it is in the cross direction.In newspaper work it is common to use mats which provide from aboutone-half to about one and one-fourth inches in cross-wise shrinkage foramat measuring about fifteen and nine-sixteenths inches wide andtwenty-one and three-quarter inches long between the limitsof the typearea, where the drying is done in two steps, as will bedescribed later.Where only one drying step is involved, it is desirable to allow for aslight decrease in shrinkage over that ordinarily anticipated, so thatwhere a given mat may have a characteristic shrinkage of one andone-eighth inches it will shrink about one inch when combined with thebacking material described.

The printing form 10 with the mat, backing and the molding combinationin place is set on a table 23 and passed between the nip of a pair ofpressure rolls 24 and 26. One or both of the rolls 24 and 26 is madevertically adjustable to compensate for different thicknesses ofprinting forms. The pressures used in connection with the backedstereotype mat are substantially the same as those used presently inmolding stereotype mats without any backing. It is ditiicult to measurethe exact pressure employed, as the contacting areas of the roll towhich the pressure is applied cannot be accurately ascertained. However,it is generally accepted that the molding pressures required for goodreproduction are on the order of 2000 to 4000 pounds per square inchover the printing areas and may be considerably higher. It should alsobe understood that although the described method of molding stereotypemats is the most common method, the present invention is equallyapplicable to mat molding procedures involving the use of directpressure with flat platens.

As pressure is applied to the assembly in the lockup, the mat 19 iscompressed into the space between the raised, printing characters andforms a sharply defined reproduction of the printing characterscontained in the lockup or form 10. The backing 21 is moisture permeableand, therefore, is capable of absorbing any moisture expressed from thestereotype mat 19. The backing 21 is considerably more compressible thanthe mat 19 and, as a result of the pressing, the thickness of thebacking 21 is considerably reduced over the printing areas. Underordinary molding pressurm, the thickness of the backing may be reducedby a factor of four or five times over the printing areas, so thatabacking originally .050 inch in thickness may end up as a compressedbacking. of about .010 inch, whereas in the nonprinting areas thebacking may be compressed to about .040 inch, thereby providing a spacedepth between the level of the nonprinting areas and the base; of theprinting areas of b ut 39 h,-

The described backing material is able to conform accurately to thecontour of the back of the mat 19 during, application of pressure. Atthe same time the backing 21- becomes quite securely bonded to the backofthe mat 19 over'the areas of the mat which are subjected to the highmolding pressures. Although this bonding may particularly thehydrophilic copolymer derivative, suchas the sodium salt ofstyrene-maleic anhydride copolymer.

In the stated condition, however, the overall characteristicsof thebacking are such that it is able to withstand the molding pressure anddoes not collapse during the pressing operation. The phenolic resin inthe backing is in asuificient state of cure to provide adequate rigidityto sustain the loads imposed during the pressing operation. Furthermore,the styrene-maleic anhydride copolymer provides sufiicient track toprovide the necessary bonding of the backing 21 to the mat 19.

A portion of the backed mat, after removal from the molding apparatus,is illustrated in enlarged form in FIGURE 4. As seen in that drawing,the face of the mat 19 is depressed in conformity to the shape of thelockup, as seen at 28and 29, depending upon the pressure, moldingcombination, and the space areas and depths available in the originallockup.

In the nonprintingareas, as for example in the area. 29, theremarkableresiliency of the backing 21 causes the backing to recovermuch of its original thickness after removal of. the molding pressure,as indicated at 33. Yet in the areas above the printing surfaces, suchas the area 31, the backing takes a more permanent set but still retainsthe high degree of flexibility and moisture permeability. The result isthat the backed mat produced by the molding operation has a generallyplanar rear surface 35 which may be readily conformed to the surface ofthe dryer. Further, the backing material is packed into those smallnonprinting areas that a hand packer does not even touch in the ordinaryprocess of stereotype mat forming.

After the removal from the molding apparatus, the composite mat andbacking is then ready for drying and for setting of the resinousimpregnate. For the manufacture of curved plates, the mat 19 and itsbacking 21 are given a uniform curvature by introducing the mat into aconventional dryer assembly. One type of dryer or scorcher, as it isusually called, is illustrated in FIG.

5 of the drawings and comprises an asbestos covered.

drum 34 in which a plurality of heating elements 36 are disposed beneaththe asbestos surface. A cover or chamber 37 having a perforated innerface 38 and a plurality of heating elements 40 is hinged to the drum 34at the hinge 39. The backed mat is held against the inner face 38 byapplying a vacuum to the back of the composite mat through theperforations in the face 38. The cover is also heated by means of spacedheating elements contained therein.

The vacuum applied to the mat holds the mat in contact with the face 38and spaces the face of the mat slightly from the asbestos coveredsurface of the drum 34 when the cover 37 is in its closed position.Thus, the vacuum serves not only to hold the mat in position, but alsoholds the back of the mat against a smooth surface so as to provide auniformly curved reference surface for the mat. The temperature at theback of the dryer is ordinarily on the order of 250 to 400 F. As theheat is applied moisture is driven from the mat and passes through theporous backing material and is thereupon vented. In this respect, it isparticularly important in a shrink type matthat the resinous impregnateshould not become cured or rigid until substantially alLof: the desiredshrinkage of the mat and backing, through removal' 9" of the moisture,has taken place. Consequently, the thermosetting resins selected shouldbe of a type that will become substantially cured throughout at atemperature somewhere near the upper range of the drying temperaturewhich will prevail throughout the mat when essentially all of themoisture has been removed. Additional advantage is had with thedescribed materials in that the styrene-maleic anhydride copolymerhardens under the temperatures of the scorcher.

Where only one drying step is used, with the described materials atreatment time of 3 to 6 minutes at temperatures of 250 to 400 F. willsufiice to drive 011 the moisture and set the irreversible resinssufiiciently under moisture conditions normally prevailing in the mat.The control of shrinkage is facilitated by operating at a lower vacuum,on the order of one and one-half inches of mercury during the firstminute or two and then increasing it to a value of five to six inches ofmercury when substantially all of the moisture has been driven oif. Whena pre-drying step is employed in conjunction with the final drying andforming, times of about 10 to 90 seconds at temperatures of about 150 to300 F. may be employed during the pre-drying to initiate shrinkage ofthe composite mat without substantial change in the condition of theirreversible resin.

During the drying operation the thermosetting resin in the backingshould be cured suificiently s that it will resist collapse under thetemperature and pressures encountered in the casting of the stereotypeplate. It is believed that with impregnates of the described type a cureof at least 95 percent throughout the backing should be achieved. Inother words, the thermosetting resin extractibles in the sheet shouldnot exceed about 5 percent after scorching.

The extractibles content can be readily determined by the standardA.S.'I.M. test (D494 -4l) which involves taking a known weight of atypical sample of the cured sheet material in finely comminuted form,and placing this sample in a Soxhlet apparatus where it is extractedwith hot acetone for a period of four hours. The acetone is thenevaporated under controlled conditions and the sample removed, so thatthe residue constitutes the extractible materials which have beendissolved by the acetone.

Upon removal of the backed mat from the dryer, the mat is ready forinsertion in the casting box. The final form of the mat is illustratedin FIGURE 6 of the drawings and includes the paperboard mat 19 having acasting face 1% of concave shape and the backing 21 in which theresinous material has become set and rigidi-fied by the heat treatmentin the dryer. Composite mats of this type have been found to adequatelyresist collapse under type casting pressures on the order of 15 to 25pounds per square inch.

In addition to the foregoing manner of forming and using a backing ofthe type described, it has been found that definite advantages aregained by employing further precautions. An improvement is noted in theeffectiveness of the backing sheet if the backing sheet, just prior toits use, is at equilibrium in a relative humidity of 45 to 65 percent.Furthermore it has been found advantageous to use the low range of heatin the scorcher, about 250-300 F., in order to achieve best results withthe described backing.

The blend of resinous material described above affords definiteimprovement over previou backing sheets, particularly with respect to animproved attachment of the several plies to each other and to thestereotype mat, and in providing an improved resiliency in the backingto thereby achieve better plate reproduction with substantially betterspace-depth characteristics.

Although described with respect to particular materials, it should beunderstood that other suitable materials having the describedcharacteristics might be employed without departing from the principlesof this in below about-20 C. and being capable of becoming sub-1.

stantially cured at temperatures of between 250 and 400 F., whereby saidbacking is moisture permeable and said resinous material is subject tolittle change in physical characteristics below temperatures of about 20C., and said resinous material becomes rigid at temperatures of about350 F.

2. A backing for a stereotype mat comprising a plurality of creped,cellulosic sheets impregnated with about 15 to 75 percent by weight, ona dry basis, of a substance including a thermosetting resin which is ina low state of polymerization and substantially completely waterdispersible in such state, said thermosetting resin .compris ing fromabout 65 to percent of a phenol-aldehyde resin, by dry weight of thetotal solids content of said substance, from about 5 to 35 percent, bydry weight, of a styrene-maleic anhydride copolymer, and about 2 to 10percent, by dry weight, of a water soluble polyvinyl alcohol, saidsubstance being substantially stable at temperatures below about 20 C.,and said substance being capable of becoming substantially cured attemperatures of between 250 and 400 '-F., whereby said backing ismoisture permeable and said substance is subject to little change inphysical characteristics below temperatures of about 20 C. but becomessubstantially cured at temperatures of about 350 F.

3. A backing for a stereotype mat comprising from 3 to 20 plies ofcreped, cellulosic sheets impregnated with about 15 to 75 percent, byweight on a dry basis, of a substance including a one-stepphenol-formaldehyde resin which is in a low state of polymerization andsubstantially completely water dispersible in such state, saidcellulosic sheets having an uncreped basis weight of from 5 to 10 poundsper 480 sheets each 24 by 36 inches and a crepe ratio of from 1.3 to2.5, said phenol-formaldehyde resin comprising from about 65 to 95percent, by dry weight of the solids content of said substance, and fromabout 5 to 35 percent, by dry weight, of a sodium salt of styrene-maleicanhydride copolymer, said substance having a pH of from 7.0 to 7.3, saidphenol formaldehyde resin having a dilutability within the range of from2.0 parts of water to 1.0 part of resin to about 6.0 parts of Water to1.0 part of resin and being sub stantially stable at temperatures belowabout 20 C., said substance being capable of becoming substantiallycured at temperatures of between 250 and 400 F.

4. A composition which is particularly adaptable for use in impregnatinga low density, compressible paper sheet to form a backing for astereotype flong, said composition comprising a resinous substanceincluding from about 65 to 95 percent, by dry weight of the solidscontent, of a phenol-aldehyde resin in a low state of polymerization andwhich is substantially completely Water dispersible, from about 5 to 35percent, by dry weight, of a sodium salt of styrene-maleic anhydridecopolymer, and about 2 to 10 percent, by dry Weight of a water solublepolyvinyl alcohol, said resinous substance being substantially stable attemperatures below about 20 C., and said resinous substance beingadapted to be substantially cured at temperatures of between 250 and 400F.

5. A composition which is particularly adaptable for use in impregnatingmulti-ply, crepe paper sheets in the formation of a backing for astereotype flong, said: com;

position comprising a resinous substance including. from about 65 to 95percent, by dry weight of the solids content of' a thermosettingone-stage phenol-aldehyde resin in a low state of polymerization andwhich is substantially completely water dispersible insuch state, fromabout 5 to 35 percent, by dry weight, of an alkali-salt of styrenemaleicanhydride copolymer, water in anamount sufficient to produce asolidscontent of from 32 to 34 percent, and sulfamic acid in anamountsufiicient to adjust the pH of the composition to a substantiallyneutral condition, said composition being substantially stable in itsstate of polymerization attemperatures below about 20 (3;, and saidcomposition being capable of being 12 substantially completely.polymerized at temperatures: be tweemZSO. and,400?

References Citedin the file of this patent UNITED STATES PATENTS

1. A BACKING FOR A STEREOTYPE MAT COMPRISING A PLURALITY OF CREPED,CELLULOSIC SHEETS IMPREGNATED WITH FROM ABOUT 15 TO 75 PERCENT, BYWEIGHT ON A DRY BASIS, OF A RESINOUS MATERIAL INCLUDING FROM ABOUT 65 TO95 PERCENT OF A PHENOL-ALDEHYDE RESIN AND 5 TO 35 PERCENT OF ASTYRENEMALEIC ANHYDRIDE COPOLYMER, SAID PHENOL-ALDEHYDE RESIN BEING IN ASTATE OF LOW POLYMERIZATION AND SUBSTANTIALLY COMPLETELY WATERDISPERSIBLE IN SUCH STATE, SAID PHENOLALDEHYDE RESIN BEING SUBSTANTIALLYSTABLE AT TEMPERATURES BELOW ABOUT 20*C. AND BEING CAPABLE OF BECOMINGSUBSTANTIALLY CURED AT TEMPERATURES OF BETWEEN 250* AND 400* F., WHEREBYSAID BACKING IS MOISTURE PERMEABLE AND SAID RESINOUS MATERIAL IS SUBJECTTO LITTLE CHANGE IN PHYSICAL CHARACTERISTICS BELOW TEMPERATURES OF ABOUT20*C., AND SAID RESINOUS MATERIAL BECOMES RIGID AT TEMPERATURES OF ABOUT350*F.